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Research Summary:
Paper: The thermal and dielectric properties of high performance cyanate ester resins/microcapsules composites
Authors: Li Yuan, Guozheng Liang, Aijuan Gu
Published: 13 July 2010 in Polymer Degradation and Stability
  • Many different methods have been applied in order to improve the properties of cyanate ester. The addition of epoxy filled, poly(urea-formaldehyde) microcapsules (MCE’s) to pure cyanate ester is shown to improve the thermal and dielectric properties of the material. Improvements in these properties were examined using dynamic mechanical analysis (DMA) , and thermo-gravimetric analysis (TGA).
  • The materials used in the experiment were Bisphenol A dicyanate ester, and the (MCE’s).
  • To prepare the composite, the MCE’s were stirred into the cyanate ester at 130C and poured into a mould after degassing. The cure schedule was 120C for 1 hour, 150C for 1hour, 180C for 2 hours, and 200C for 2 hours.
  • Thermal stability measurements were made using the DMA and the TGA. The materials morphology was captured by a scanning electron microscope (SEM). Dielectric measurements were made using a dielectric analyzer after subjecting the samples to 100C water and air for 100 hours, and FTIR spectroscopy was used to determine the chemical structure of the material.
  • The TGA showed a decrease in the thermal stability of each sample with increasing amounts of MCE’s. This is mainly due to the fact that materials from the MCE’s react with the un-bonded cyanate group to from a lower density cross-linking structure.
  • Above 400C, the sample with 2% wt MCE’s showed an increase in thermal stability. This is due to the ability of the MCE’s to catalyze the conversion of cyanate groups into triazine rings during curing.
  • The DMA showed a trend of lower glass transition temperature (Tg) with increased MCE loading, except for 2% MCE cyanate ester, which had the highest Tg.
  • The dielectric analyzer showed an increasing dielectric constant with increased MCE loading, except for 2% MCE cyanate ester, which had the lowest dielectric constant. This is due to the increased amount of reacted and unreacted MCE, both of which have higher dielectric constants than the pure cyanate ester. The 2% wt MCE cyanate ester balances the increased formation of triazine rings with the side reactions of the MCE’s to produce a material with a slightly higher dielectric constant.
  • Dielectric loss decreases as the loading of MCE’s increases, since the polymer matrix becomes harder to move as the conversion of cyanate groups increases.
  • Dielectric constant after the samples were subjected to boiling water for 100 hours increased with the loading of MCE, except for the 2% wt sample, which retained the lowest dielectric constant. This is due to the fact the MCE’s contain more moisture than the pure cyanate ester, but the conversion of cyanate groups lowers the dielectric constant of the material.
  • Dielectric constant of the cyanate ester after being subjected to 100C air for 100 hours increased with increasing MCE loading, except for 2%wt MCE, which retained a lower dielectric constant than pure cyanate ester.
  • Despite the fact that most loadings, especially higher loadings, of MCE’s to cyanate ester tend to decrease the thermal and dielectric properties of the material, the addition of 2%wt MCE to cyanate ester can slightly improve these properties both under normal conditions, and when subject to hot air and water.